diff --git a/configure.ac b/configure.ac
index 66f9dc65..b9b995c3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,7 +1,7 @@
 #                                               -*- Autoconf -*-
 # Process this file with autoconf to produce a configure script.
 
-AC_PREREQ([2.71])
+AC_PREREQ([2.61])
 AC_INIT([IPhreeqc], [3.7.6-16410], [charlton@usgs.gov])
 AC_CONFIG_AUX_DIR([config])
 AC_CONFIG_MACRO_DIR([m4])